Hmm, caching has never caused problems with split DNS for me, but it’s really hard to debug what was going on with your setup. Split DNS is really common and is the preferred way to solve this, so most browsers have logic to handle it. You might have had something misconfigured, but unfortunately it’s really hard to diagnose.
AKA, split DNS. Doing it this way is a bit cleaner than hairpin NAT as mentioned in other comments, but both options work fine in a home network.
I mean the original lawsuit was for aggressively bundling Internet Explorer and kneecapping other browsers. Which sure sounds a lot like a minor variation on what they’ve been doing with Edge and Bing for a while now, without consequences. Antitrust enforcement is not something I have a lot of confidence in for the foreseeable future.
The message you’re reading applies to the checkbox above for encryption, not the preferences url. The preferences key only needs to be set if you want to encrypt the configuration URL, it doesn’t affect what OP wants to do.
My memory is a bit fuzzy because I switched to Searxng after playing with Whoogle briefly, but I thought Whoogle stored preferences in a cookie or something similar; the preferences URL is for when you want to transfer the preferences for your current machine to another. So OP is misunderstanding what it’s for.
OP: if your preferences aren’t sticking, are you maybe blocking cookies entirely or something? I’m pretty sure you shouldn’t need to do anything with the preferences URL for your preferences to stick if everything is set up correctly, it’s only for transferring your preferences to another machine.
As another poster pointed out, it sounds like you want more of a mail search and archival tool than a mail server. I would suggest you pull the emails in maildir format from Google Takeout, and then index/search them with the amazing Notmuch. Notmuch is way more capable than Gmail search ever has been. Look at the Arch Wiki page page as well for info, the official docs are a bit obtuse but it’s not actually hard to use.
Impossible to say, could be the app is doing something funky, could be iOS, could be lotta things.
I will note, my preferred solution is to do none of the above, and I only do split DNS for one particular service. I much prefer just using an always on Wireguard VPN that is set to only route traffic to my internal subnets and to use my internal DNS server. Then I just use internal names. Wireguard basically runs at line rate on my setup, so half the time I don’t even turn it off at home. This also gives you the option to use DNS ad blocking (eg adguard) on the go.